Smectic liquid crystal phases

ABSTRACT

Compounds of the formula I 
     
         R.sup.1 -A.sup.1 -A.sup.2 -R.sup.2                         I 
    
     wherein 
     R 1  and R 2  are each alkyl with 1-15 C atoms, and wherein one or two non-adjacent CH 2  groups can also be replaced by --O--, --S--, --CO--, --O--CO--, --CO--O--, --CO--S--, --S--CO--, --CHHalogen--, --CHCN-- and/or --CH═CH--, 
     A 1  is 1,4-phenylene, trans-1,4-cyclohexylene or a single bond and 
     A 2  is ##STR1##  in which Z is --O--CO--, --CO--O--, --S--CO--, --CO--S--, CH 2  O--, --OCH 2  -- or --CH 2  CH 2  --, with the proviso that, if A 1  is a single bond, A 2  is ##STR2##  are suitable as components of chirally tilted smectic liquid crystal phases.

This is a continuation of application Ser. No. 018,947, filed Dec. 24, 1986, now abandoned.

The invention relates to the use of compounds of the formula I

    R.sup.1 -A.sup.1 -A.sup.2 -R.sup.2                         I

wherein

R¹ and R² are each alkyl with 1-15 C atoms, and wherein one or two non-adjacent CH₂ groups can also be replaced by --O--, --S--, --CO--, --O--CO--, --CO--O--, --CO--S--, --S--CO--, --CHHalogen--, --CHCN--and/or --CH═CH--,

A¹ is 1,4-phenylene, trans-1,4-cyclohexylene or a single bond and

A² is ##STR3## in which Z is --O--CO--, --CO--O--, --S--CO--, --CO--S--, --CH₂ O--, --OCH₂ --or --CH₂ CH₂ --, with the proviso that if A¹ is a single bond,

A² is ##STR4## as components of chirally tilted smectic liquid crystal phases, and chiral tilted smectic liquid crystal phases containing compounds of the formula I.

Chiral tilted smectic liquid Crystal phases with ferroelectric properties can be prepared by adding a suitable chiral doping substance to base mixtures with one or more tilted smectic phases (L. A. Beresnev et al., Mol. Cryst. Liq. Cryst. 89, 327 (1982); H. R. Brand et al., J. Physique 44 (lett.), L-771 (1983)). Such phases can be used as dielectrics for rapidly switching displays based on the principle of SSFLC technology described by Clark and Lagerwall (N. A. Clark and S. T. Lagerwall, Appl. Phys. Lett. 36, 899 (1980); U.S. patent Specification No. 4,367,924) on the basis of ferroelectric properties of the chirally tilted phase. In this phase, the longitudinally stretched molecules are arranged in layers, the molecules having a tilt angle relative to the normal of the layers. On advancing from layer to layer, the tilt direction changes by a small angle in respect of an axis vertical to the layers, so that a helix structure is formed. In displays based on the principle of SSFLC technology, the smectic layers are arranged vertical to the plates of the cell. The helical arrangement of the tilt direction of the molecules is suppressed by a very small distance between the plates (about 1-2 μm). The longitudinal axes of the molecules are thereby forced to align themselves in a plane parallel to the plates of the cell, which means that two distinct tilt orientations result. By applying a suitable alternating electrical field, a system can be switched back and forth between these two states in the liquid crystal phase which exhibits spontaneous polarization. This switching process is considerably more rapid than in conventional twisted cells (TN-LCDs) based on nematic liquid crystals.

A great disadvantage for many applications of the materials currently available with chirally tilted smectic phases (such as, for example, Sc*, but also S_(H) *, S_(I) *, S_(J) *, S_(K) *, S_(G) * and S_(F) *) is their low chemical, heat and light stability. Another adverse property of displays based on the chirally tilted smectic mixtures currently available is that values of the spontaneous polarization are too low, so that the switch time properties of the displays are adversely influenced and/or the pitch and/or the tilt and/or the viscosity of the phases do not meet the requirements of display technology. Moreover, the temperature range of the ferroelectric phases is usually too small and is predominantly at temperatures which are too high.

It has now been found that the use of compounds of the formula I as components of chirally tilted smectic mixtures can substantially reduce the disadvantages mentioned. The compounds of the formula I are thus outstandingly suitable as components of chirally tilted smectic liquid crystal phases. In particular, chirally tilted smectic liquid crystal phases which are particularly chemically stable, have favourable ferroelectric phase ranges and favourable viscosity values, in particular broad Sc* phase ranges, have an outstanding behaviour on supercooling down to temperatures below 0° C. without crystallization occurring and have high spontaneous polarization values for such phases can be prepared with the aid of these compounds. P is the spontaneous polarization in nC/cm².

Although it has been disclosed that, among the compounds of the formula I, the 5-n-alkyl-2-(4-n-alkoxyphenyl)pyrimidines can be used as components of smectic liquid crystal materials for thermography (East German Patent 148,676) or as components of guest-host mixtures in electrooptical assemblies (East German Patent 129,699), no information at all is given there which indicates that these compounds can be used as components of chirally tilted smectic mixtures for ferroelectric displays based on, for example, the SSFLC technology described by Clark and Lagerwall.

The compounds of the formula I have a wide range of applications. Depending on the choice of substituents, these compounds can be used as base materials from which liquid crystal smectic phases are predominantly composed; however, it is also possible for compounds of the formula I to be added to liquid crystal base materials from other classes of compounds, for example in order to vary the dielectric and/or optical anisotropy and/or the viscosity and/or the spontaneous polarization and/or the phase ranges and/or the tilt angle and/or the pitch of such a dielectric.

The invention thus relates to the use of the compounds of the formula I as components of chirally tilted smectic liquid crystal phases. The invention furthermore relates to chirally tilted smectic liquid crystal phases containing at least one compound of the formula I and liquid crystal display elements, in particular ferroelectric electrooptical display elements, containing such phases.

The phases according to the invention contain preferably at least three and in particular at least five compounds of the formula I. Particularly preferred chirally tilted smectic liquid crystal phases according to the invention are those in which the achiral base mixture contains, in addition to compounds of the formula I, at least one other component with a negative or comparatively low positive dielectric anisotropy. This/these other component(s) of the achiral base mixture can make up 1 to 50%, preferably 10 to 25%, of the base mixture. Suitable further components with a comparatively low positive or negative dielectric anisotropy are compounds of the formula II, which includes the compounds of the part formulae IIa to IIi: ##STR5##

R⁴ and R⁵ are in each case preferably straight-chain alkyl, alkoxy, alkanoyloxy or alkoxycarbonyl with in each case 3 to 12 C atoms. X is preferably O. In the compounds of the formulae IIa, IIb, IId, IIe, IIf and IIg, it is also possible for a 1,4-phenylene group to be laterally substituted by halogen or CN, particularly preferably by fluorine.

Particularly preferred compounds are those of the part formulae IIa, IIb, IId and IIf, wherein R⁴ and R⁵ are each straight-chain alkyl or alkoxy with in each case 5 to 10 C atoms.

Particularly preferred individual compounds are shown in the following table: Formula

    ______________________________________                                         Formula     R.sup.4     R.sup.5    X                                           ______________________________________                                         IIa         n-Decyloxy  n-Heptyloxy                                                                               ◯                               IIa         n-Hexyloxy  n-Decyloxy ◯                               IIa         n-Octyloxy  n-Heptyl   ◯                               IIa         n-Octyloxy  n-Pentyl   ◯                               IIa         n-Decyloxy  n-Heptyl   ◯                               IIa         n-Decyloxy  n-Pentyl   ◯                               IIf         n-Pentyl    n-Pentyl   ◯                               IIf         n-Pentyl    n-Hexyl    ◯                               ______________________________________                                    

The compounds of the part formulae IIc, IIh and IIi are suitable as additives for lowering the melting point and are usually added to the base mixtures in an amount of not more than 5%, preferably 1 to 3%. R⁴ and R⁵ in the compounds of the part formulae IIc, IIh and IIi are preferably straight-chain alkyl with 2 to 7, preferably 3 to 5, C atoms. Another class of compound which is suitable for lowering the melting point in the phases according to the invention is that of the formula ##STR6## wherein R⁴ and R⁵ have the preferred meaning given for IIc, IIh and IIi.

Suitable further components with negative dielectric anisotropy are furthermore compounds containing the structural element A, B or C ##STR7##

Preferred compounds of this type correspond to the formulae IIIa, IIIb and IIIc: ##STR8##

R' and R'' are each preferably straight-chain alkyl or alkoxy groups with in each case 2 to 10 C atoms. Q¹ and Q² are each 1,4-phenylene, trans-1,4-cyclohexylene, 4,4'-biphenylyl, 4-(trans-4-cyclohexyl)-phenyl or trans,trans-4,4'-bicyclohexyl, or one of the groups Q¹ and Q² is also a single bond.

Q³ and Q⁴ are each 1,4-phenylene, 4,4'-biphenylyl or trans-1,4-cyclohexylene. One of the groups Q³ and Q⁴ can also be 1,4-phenylene, at least one CH group being replaced by N. R''' is an optically active radical with an asymmetric carbon atom of the structure ##STR9## Particularly preferred compounds of the formula IIIc are those of the formula IIIc': wherein A is 1,4-phenylene or trans-1,4-cyclohexylene and n is 0 or 1.

The compounds of the formula I include dinuclear and trinuclear materials. Of the dinuclear materials, which are preferred, those wherein R¹ is n-alkyl with 7 to 10 and in particular 7 to 9 C atoms are preferred. Compounds of the formula I where R¹ =n-heptyl or n-octyl impart good low temperature properties to the phases according to the invention, whilst the corresponding compounds with R¹ =n-nonyl are capable of increasing the S_(A) /S_(C) transition temperature of the phases according to the invention.

Preferred phases according to the invention contain at least one compound of the formula I wherein R¹ is n-nonyl and at least one compound of the formula I wherein R¹ is n-heptyl or n-octyl. Particularly preferred phases according to the invention are those containing compounds of the formula I wherein R¹ is n-heptyl, n-octyl or n-nonyl. R² in the dinuclear compounds of the formula I is preferably n-alkoxy with 6 to 12, in particular with 7 to 10, C atoms. The phases according to the invention preferably contain at least one compound of the formula I wherein R² is n-hexyloxy, n-heptyloxy or n-octyloxy (preferably n-heptyloxy or n-octyloxy) and at least one compound of the formula I wherein R² is n-nonyloxy or n-decyloxy. The sum of the C atoms in the groups R¹ and R² of the preferred dinuclear compounds of the formula I is preferably 15 or more, particularly preferably in the range from 15 to 20. Particularly preferred individual compounds of the formula I are listed in the following table:

    ______________________________________                                         R.sup.1       R.sup.2    A.sup.1                                               ______________________________________                                         n-Nonyl       n-Nonyloxy --                                                    n-Nonyl       n-Hexyloxy --                                                    n-Octyl       n-Decyloxy --                                                    n-Octyl       n-Octyloxy --                                                    n-Octyl       n-Heptyloxy                                                                               --                                                    n-Heptyl      n-Decyloxy --                                                    n-Heptyl      n-Nonyloxy --                                                    n-Pentyloxy   n-Octyl                                                                                    ##STR10##                                            n-Hexyloxy    n-Hexyl                                                                                    ##STR11##                                            n-Hexyloxy    n-Pentyl                                                                                   ##STR12##                                            n-Pentyloxy   n-Nonyl                                                                                    ##STR13##                                            n-Octyloxy    n-Octyl                                                                                    ##STR14##                                            ______________________________________                                    

Compounds of the formula I which are furthermore preferred are those wherein R¹ is n-alkyl with 7 to 10 C atoms and R² is n-alkanoyloxy, n-alkoxycarbonyl or n-alkylthio with in each case 5 to 10 C atoms.

The phases according to the invention preferably contain at least one trinuclear compound of the formula I and/or one compound of the formula I wherein R² is n-alkylthio. These phases are distinguished by particularly high S_(C) /S_(A) transition temperatures.

However, other preferred phases according to the invention are those which merely contain compounds of the formula I in which A¹ is a single bond. These phases are distinguished by particularly favourable low-temperature behaviour and particularly low viscosity values. Other preferred phases according to the invention are those which contain compounds of the formula I in which at least one group R¹ or R² is a branched alkyl or alkoxy radical. These phases likewise exhibit favourable low-temperature behaviour.

R¹ and R² independently of one another are each preferably alkyl, alkoxy, alkanoyl, alkanoyloxy, alkoxycarbonyl or alkoxycarbonyloxy, each preferably having 5 to 12, in particular 6 to 10, C atoms. Alkyl and alkoxy are particularly preferred. One of the groups R¹ and R² is preferably alkyl. A particularly preferred combination is one in which R¹ is alkyl and R² is alkoxy, as well as one in which R¹ is alkoxy and R² is alkoxy. R¹ and R² groups with a straight-chain alkyl radical are particularly preferred.

Phases according to the invention which are furthermore preferred are those containing at least one dinuclear compound of the formula I wherein R¹ is n-alkyl with 7 to 10 C atoms and R² is --CH₂ O--(CH₂)_(p) --CH₃ or --O--(CH₂)_(q) --O--(CH₂)_(r) --CH₃. p is preferably 4 to 10, in particular 5 to 5. q is preferably 1 or 2, particularly preferably 2. r is 4 to 10, particularly preferably 5 to 9. q can also be >2, for example 3 to 5.

is preferably ##STR15## and particular preferably ##STR16##

A¹ is preferably a single bond or, where A² is ##STR17## 1,4-phenylene.

Z is preferably --CO--O--, --O--CO--or --CH₂ CH₂.

Other preferred meanings for A² are ##STR18##

Phases according to the invention which are furthermore preferred are those containing at least one compound of the formula ##STR19## wherein R_(a) is alkyl with 3 to 12 C atoms and R_(b) is alkyl or alkoxy with in each case 5 to 12 C atoms. R_(a) and R_(b) together contain at least 15 C atoms, preferably at least 17 C atoms.

A particularly preferred chiral tilted smectic liquid crystal phase with at least one compound of the formula I according to claim 1 is characterized in that it contains a liquid crystal component with negative dielectric anisotropy, and in particular is a phase according to the invention, characterized in that it contains at least one compound containing the structural element A, B or C as the component with negative dielectric anisotropy. ##STR20##

A particularly preferred phase according to the invention is furthermore characterized in that it contains at least one compound of the formula II

    R.sup.4 'A.sup.1 --COX--A.sup.2 --R.sup.5                  II

wherein

R⁴ and R⁵ are each alkyl with 1-15 C atoms, it also being possible for one or two non-adjacent CH₂ groups to be replaced by --O--, --CO--, --O--CO--, --CO--O-- and/or --CH=CH--,

X is O or S and

A¹ and A² are each 1,4-phenylene or trans-1,4-cyclohexylene, or one of the groups A¹ and A² is optionally also 4,4'-biphenylyl or trans,trans-4,4'-bicyclohexyl.

Other preferred ferroelectric phases according to the invention are those which contain at least one compound of the formula V

    R.sup.1 --Q.sup.1 --A--(Q.sup.2).sub.q --R.sup.2           V

wherein

R¹ and R² independently of one another are each a straight-chain alkyl group having 1 to 15 C atoms, wherein furthermore one or more non-adjacent adjacent CH₂ groups may be replaced by --O--, --S--, --CO--, --CHCH₃ --O--, --CHCH₃ --, --CH--halogen--, --CHCN--, --O--CO--, --O--COO--, --CO--O--and/or --CH═CH--,

A is ##STR21## q is 0 or 1, Q¹ and Q² independently of one another are each --(A^(o) --Z^(O))_(p) --,

wherein

A^(O) is 1,4-cyclohexylene which is unsubstituted or monosubstituted or polysubstituted by halogen atoms, CH₃ groups and/or nitrile groups, and wherein furthermore one or two non-adjacent CH₂ groups may be replaced by --O--and/or --S--and/or ##STR22## grouping may be replaced by ##STR23## or is 1,4-phenylene which is unsubstituted or monosubstituted or polysubstituted by halogen atoms, CH₃ groups and/or nitrile groups, wherein furthermore one or more CH groups may be replaced by N (Ph), and one of the radicals A^(o) may furthermore be 2,6-naphthylene (Na) or tetrahydro-2,6-naphthylene (4H-Na), if appropriate substituted by halogen or CN,

Z^(o), Z¹ and Z² independently of one another are each --CO--O--, --O--CO--, --CH₂ O--, OCH₂ --, --CH₂ CH₂ --, --CHCNCH₂ --, --CH₂ --CHCN--or a single bond, and

p is 1, 2 or 3, or, where A is tetra- or octahydrophenanthrene, also O, and where

A is ##STR24## at least one group Z^(o) is --CHCNCH₂ --or --CH₂ CHCN--and/or at least one CH₂ group in at least one of the groups R¹ and R² is replaced by --CHCN--.

The compounds of the formula V can have straight-chain or branched wing groups R¹ and/or R². Compounds possessing branched wing groups can be used in the form of the racemate or as optically active compounds. Achiral base mixtures of compounds of the formula V and, if appropriate, further achiral components can be doped with chiral compounds of the formula I or additionally with other chiral compounds, in order to obtain chirally tilted smectic phases.

Particularly preferred smaller groups of compounds are those of the formula V1 to V18: ##STR25##

Another particularly preferred smaller group of compounds comprises those of the formulae V19 to V22:

    R.sup.1 --A.sup.o --Cy--(CH.sub.2).sub.r --CHCN--C.sub.s H.sub.2s+1 V 19

    R.sup.1 --A.sup.o --A.sup.o --A.sup.o --Cy--(CH.sub.2).sub.r --CHCN--C.sub.s H.sub.2s+1                                V 20

    R.sup.1 --A.sup.o --A.sup.o --CHCN--CH.sub.2 --Cy--R.sup.2 V 21

    R.sup.1 --A.sup.o --A.sup.o --CH.sub.2 --CHCN--Cy--R.sup.2 V 22

wherein

r is 0, 1, 2 or 3 and

(r+s) is 1 to 14.

Compounds of the formula I which do not possess any S_(c) phases are likewise suitable as components of smectic phases according to the invention.

The phases according to the invention may furthermore contain compounds of the formula ##STR26## wherein R¹ and R² have the meaning given in the case of formula V.

All components of the phases according to the invention are either known or can be prepared in a manner known per se, analogously to known compounds.

The phases according to the invention are prepared in a manner which is customary per se. As a rule, the components are dissolved in one another, advantageously at elevated temperature.

The liquid crystal phases according to the invention can be modified by suitable additives so that they can be used in all the types of liquid crystal display elements hitherto disclosed.

The following examples are intended to illustrate the invention without limiting it. Percentages above and below are percentages by weight; all the temperatures are stated in degrees Celsius. The values given for spontaneous polarization are applicable to room temperature. The symbols are furthermore as follows: Cr: crystalline solid state, S: smectic phase (the index characterizes the phase type), N: nematic state, Ch: cholesteric phase, I: isotropic phase. The figure between two symbols indicates the transition temperature in degrees Celsius.

EXAMPLE 1

A liquid crystal phase consisting of 25% of 2-p-decyloxyphenyl-5-heptylpyrimidine, 25% of 2-p-nonyloxyphenyl-5-nonylpyrimidine, 10% of 2-p-hexyloxyphenyl-5-nonylpyrimidine, 10% of 2-p-nonyloxyphenyl-5-heptylpyrimidine, 11% of 2-p-octyloxyphenyl-5-heptylpyrimidine, 11% of 2-p-heptyloxyphenyl-5-heptylpyrimidine and 8% of 2-p-hexyloxyphenyl-5-heptylpyrimidine

can be supercooled to -1° , Cr/S_(C) 11° and S_(C) /S_(A) 49°.

EXAMPLE 2

A liquid crystal phase consisting of

50% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

7% of 2-p-hexyloxyphenyl-5-nonylpyrimidine,

15% of 2-p-decyloxyphenyl-5-heptylpyrimidine,

7% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

7% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

7% of 2-p-heptyloxyphenyl-5-heptylpyrimidine and

7% of 2-p-hexyloxyphenyl-5-heptylpyrimidine

can be supercooled to 0°, Cr/S_(C) 6° and S_(C) /S_(A) 50°.

Example 3

A liquid crystal phase consisting of

25% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

25% of 2-p-decyloxyphenyl-5-heptylpyrimidine,

10% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

11% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

11% of 2-p-heptyloxyphenyl-5-heptylpyrimidine,

8% of 2-p-hexyloxyphenyl-5-heptylpyrimidine and

10% of p-hexyloxyphenyl trans-4-pentylcyclohexanecarboxylate

can be supercooled down to -3° without crystallization occurring and has an S_(C) /S_(A) of 44°.

EXAMPLE 4

A liquid crystal phase consisting of

25% of 2-p-decyloxyphenyl-5-heptylpyrimidine,

20% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

17% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

17% of 2-p-heptyloxyphenyl-5-heptylpyrimidine,

11% of 2-p-hexyloxyphenyl-5-heptylpyrimidine and

10% of p-hexyloxyphenyl trans-4-pentylcyclohexanecarboxylate

can be supercooled to -6° without crystallization occurring and has an S_(C) /N of 32°.

EXAMPLE 5

A liquid crystal phase consisting of

22% of 2-p-decyloxyphenyl-5-octylpyrimidine,

18% of 2-p-nonyloxyphenyl-5-octylpyrimidine,

18% of 2-p-octyloxyphenyl-5-octylpyrimidine,

18% of 2-p-heptyloxyphenyl-5-octylpyrimidine,

13% of 2-p-nonyloxyphenyl-5-heptylpyrimidine and

11% of p-hexylphenyl trans-4-pentylcyclohexanecarboxylate

can be supercooled to -5° and has an S_(C) /S_(A) of 46.1°, an S_(A) N of 57.6° and N/I of 67.6°.

EXAMPLE 6

A liquid crystal phase consisting of

20% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

10% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

18% of 2-p-decyloxyphenyl-5-octylpyrimidine,

15% of 2-p-octyloxyphenyl-5-octylpyrimidine,

12% of 2-p-heptyloxyphenyl-5-octylpyrimidine and

25% of p-hexyloxyphenyl trans-4-heptylcyclohexanecarboxylate

can be supercooled to 0° and has an S_(C) /S_(A) of 36.9°, an S_(A) /N of 61° and N/I of 68.5°.

EXAMPLE 7

A liquid crystal phase consisting of

12% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

20% of 2-p-decyloxyphenyl-5-octylpyrimidine,

16% of 2-p-nonyloxyphenyl-5-octylpyrimidine,

16% of 2-p-octyloxyphenyl-5-octylpyrimidine,

16% of 2-p-heptyloxyphenyl-5-octylpyrimidine,

10% of p-hexyloxyphenyl trans-4-pentylcyclohexanecarboxylate and

10% of r-1-cyano-1-(trans-4-pentylcyclohexyl)-trans-4-(trans-4-heptylcyclohexyl)-cyclohexane

has an S_(C) /S_(A) of 43.3°, an S_(A) /N of 64.5° and N/I of 75°.

EXAMPLE 8

A liquid crystal phase consisting of

12% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

20% of 2-p-decyloxyphenyl-5-octylpyrimidine,

16% of 2-p-nonyloxyphenyl-5-octylpyrimidine,

16% of 2-p-octyloxyphenyl-5-octylpyrimidine,

16% of 2-p-heptyloxyphenyl-5-octylpyrimidine,

10% of p-hexyloxyphenyl trans-4-pentylcyclohexanecarboxylate and

10% of 1-cyano-1-(trans-4-pentylcyclohexyl)-2-(trans-4-propylcyclohexyl)-ethane

has an S_(C) /S_(A) of 40.0°, an S_(A) /N of 59.9° and N/I of 72.5°.

EXAMPLE 9

A liquid crystal phase consisting of

12% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

20% of 2-p-decyloxyphenyl-5-octylpyrimidine,

16% of 2-p-nonyloxyphenyl-5-octylpyrimidine,

16% of 2-p-octyloxyphenyl-5-octylpyrimidine,

16% of 2-p-heptyloxyphenyl-5-octylpyrimidine,

10% of p-hexyloxyphenyl trans-4-pentylcyclohexanecarboxylate and

10% of 1-cyano-1-(trans-4-pentylcyclohexyl)-2-[trans-4-(trans-4-pentylcyclohexyl)-cyclohexyl]-ethane

has an S_(C) /S_(A) of 40.5°, an S_(A) /N of 60.6° and N/I of 72°.

EXAMPLE 10

A liquid crystal phase consisting of

12% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

20% of 2-p-decyloxyphenyl-5-octylpyrimidine,

16% of 2-p-nonyloxyphenyl-5-octylpyrimidine,

16% of 2-p-octyloxyphenyl-5-octylpyrimidine,

16% of 2-p-heptyloxyphenyl-5-octylpyrimidine,

10% of p-hexyloxyphenyl trans-4-pentylcyclohexanecarboxylate,

3.5% of trans-4-(trans-4-pentylcyclohexyl)-1-hexanoyloxycyclohexane and

6.5% of trans-4-(trans-4-heptylcyclohexyl)-1-octanoyloxycyclohexane

has an S_(C) /N of 49.5° nd N/I of 68.7°.

EXAMPLE 11

A liquid crystal phase consisting of

20% of 2-p-nonyloxyphenyl-2-nonylpyrimidine,

10% of 2-p-nonyloxyphenyl-2-heptylpyrimidine,

18% of 2-p-decyloxyphenyl-2-octylpyrimidine,

15% of 2-p-nonyloxyphenyl-2-octylpyrimidine,

15% of 2-p-octyloxyphenyl-2-octylpyrimidine,

12% of 2-p-heptyloxyphenyl-2-octylpyrimidine and

10of r-1-cyano-cis-4-(trans-4-butylcyclohexyl)-1-butyl-cyclohexane

has an S_(C) /S_(A) of 34.5°, an S_(A) /N of 56.6° and N/I of 66.0°.

EXAMPLE 12

A liquid crystal phase consisting of

20% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

10% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

18% of 2-p-decyloxyphenyl-5-octylpyrimidine,

15% of 2-p-nonyloxyphenyl-5-octylpyrimidine,

15% of 2-p-octyloxyphenyl-5-octylpyrimidine,

12% of 2-p-heptyloxyphenyl-5-octylpyrimidine and

10% of p-hexyloxyphenyl trans-4-pentylcyclohexanecarboxylate

is doped with various amounts of the chiral compound 1-methylheptyl p-(p-hexyloxybenzoyloxy)-benzoate. The phase transition temperatures and the spontaneous polarization values of the mixtures obtained with this are given in the following table. The values given for P are in each case for 10° below the Sc*/S_(A) * transition point. Addition of X % of the chiral doping substance

    ______________________________________                                         X      S.sub.C *    S.sub.A *   Ch  I    P                                     ______________________________________                                         0.95      40.5   65.0         69.1 0.05                                        1.95      45.5   65.1         68.9 0.12                                        3.11      41.3   65.2         68.6 0.21                                        4.07      37.3   65.0         67.7 0.33                                        4.93      29.5   64.8         66.9 0.43                                        7.36      19.7   64.7         66.1 0.60                                        9.96      --     64.5         65.2                                             ______________________________________                                    

EXAMPLE 13

The liquid crystal phase from Example 12 is doped with 1.09 (2.07) % of the chiral compound 4-(1-methyl-propoxy)-4'-cyanobiphenyl. The doped phase has an S_(C) ^(*) /S_(A) ^(*) of 42.4 (26.5), S_(A) ^(*) /Ch 65.7 (67.4) and Ch/I 68.9 (68.8).

EXAMPLE 14

The liquid crystal phase from Example 12 is doped with 1.10 (1.96) % of the chiral compound 4-(1-methyl-propyl)-4'-cyanobiphenyl. The doped phase has an S_(C) ^(*) /S_(A) ^(*) of 42.9 (26.9).

EXAMPLE 15

The liquid crystal phase from Example 12 is doped with various amounts of the chiral compound p-hexylphenyl p-(p-2-methylbutylphenyl)-benzoate. The phase transition temperatures of the mixtures thus obtained are shown in the following table:

Addition of X % of the chiral doping substance

    ______________________________________                                         X       S.sub.C *                                                                             S.sub.A *        Ch    I                                        ______________________________________                                         1.00    52.3           65.2   69.7                                             2.00    52.6           64.8   70.3                                             3.02    52.8           65.0   70.2                                             4.27    53.2           64.8   70.6                                             6.15    54.7           64.2   70.4                                             10.12   55.6           62.5   73.9                                             19.97   56.9           --     80.4                                             30.30   57.1           --                                                      40.46   54.3           --                                                      50.00   55.0           --                                                      ______________________________________                                    

EXAMPLE 16

The liquid crystal phase from Example 12 is doped with various amounts of the chiral compound p-2-methyl-butylphenyl p-(p-octylphenyl)-benzoate. The phase transition temperatures of the mixtures thus obtained are shown in the following table:

Addition of X % of the chiral doping substance

    ______________________________________                                         X       S.sub.C *       S.sub.A * Ch    I                                      ______________________________________                                         1.00    51.5           65.5   70.0                                             2.15    50.6           66.0   70.4                                             2.94    49.6           66.3   70.7                                             4.06    48.8           66.6   70.9                                             5.61    47.4           67.5   71.6                                             6.33    46.4           68.3   72.3                                             8.01    44.5           70.3   72.9                                             10.21   42.3           71.0   73.8                                             15.24   32.2           72.8   74.8                                             20.79   <0                                                                     ______________________________________                                    

EXAMPLE 17

A liquid crystal phase consisting of

13% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

22% of 2-p-decyloxyphenyl-5-octylpyrimidine,

18% of 2-p-nonyloxyphenyl-5-octylpyrimidine,

18% of 2-p-octyloxyphenyl-5-octylpyrimidine,

18% of 2-p-heptyloxyphenyl-5-octylpyrimidine and

11% of p-hexyloxyphenyl trans-4-pentylcyclohexane-carboxylate

is doped with various amounts of the chiral compound p-hexylphenyl p-(p-2-methylbutylphenyl)-benzoate. The phase transition temperatures of the mixtures thus obtained are shown in the following table:

Addition of X % of the chiral doping substance

    ______________________________________                                         X       S.sub.C *       S.sub.A * Ch    I                                      ______________________________________                                         0.5*    44.9           55.4   56.8                                             2.0*    47.0           57.1   68.4                                             5.0*    47.5           55.4   70.1                                             10.0    50.5           58.3   70.5                                             ______________________________________                                          *These mixtures can be supercooled to 0°.                         

EXAMPLE 18

A liquid crystal phase consisting of

38.3% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

2.0% of 2-p-hexyloxyphenyl-5-nonylpyrimidine,

36.1% of 2-p-decyloxyphenyl-5-heptylpyrimidine,

5.9% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

5.9% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

5.9% of 2-p-heptyloxyphenyl-5-heptylpyrimidine, and

5.9% of 2-p-hexyloxyphenyl-5-heptylpyrimidine

can be supercooled to below 0° and has an S_(C) /S_(A) of 53.5°, an S_(A) /N of 67.5° and N/I of 70°.

EXAMPLE 19

The liquid crystal phase from Example 18 is doped with various amounts of the chiral compound R-4-(5-hexylpyrimid-2-yl)-phenyl 2-chloropropionate. The phase transition temperatures and the spontaneous polarization values, at 20°, of the mixtures thus obtained are shown in the following table:

Addition of X % of the chiral doping substance

    ______________________________________                                         X      S.sub.C *    S.sub.A *   Ch  I    P                                     ______________________________________                                         3         48.1   65           68.7 1.08                                        6         41.0   64.1         68.1 2.14                                        10        34.5   63           68   3.12                                        ______________________________________                                    

The mixture doped with 10% of the chiral material shows a tilt angle of 14.3° at a pitch height of 16.2 μm, in each case at a temperature of 20°.

EXAMPLE 20

The liquid crystal phase from Example 18 is doped with various amounts of the chiral compound R-4-(5-nonyl-pyrimid-2-yl)-phenyl 2-chloropropionate. The phase transition temperatures and the spontaneous polarization values of the mixtures thus obtained are shown in the following table:

Addition of X % of the chiral doping substance

    ______________________________________                                         X      S.sub.C *    S.sub.A *   Ch  I    P                                     ______________________________________                                         3         41     68           72   0.50                                        6         34.5   68.5         71   0.71                                        10        26.5   69           69.5 0.87                                        ______________________________________                                    

EXAMPLE 21

The liquid crystal phase from Example 18 is doped with various amounts of the chiral compound R-4'-nonyloxy-biphenyl-4-yl 2-chloropropionate. The phase transition temperatures and the spontaneous polarization values of the mixtures thus obtained are shown in the following table. The values given for P are in each case for 10° below the Sc*/S_(A) * transition point.

Addition of X % of the chiral doping substance

    ______________________________________                                         X      S.sub.C *    S.sub.A *   Ch  I    P                                     ______________________________________                                         0.5       50.1   64.2         69.3 0.1                                         2         45.7   64           69   0.2                                         3         42.3   63.7         68.6 0.3                                         4         40.8   63.1         68.4 0.5                                         5         37.1   62.7         68.1 0.6                                         10        24.5   61           67.9 0.8                                         ______________________________________                                    

EXAMPLE 22

A liquid crystal phase consisting of

42% of 2-p-decanoyloxyphenyl-5-octylpyrimidine,

23% of 2-p-heptanoyloxyphenyl-5-octylpyrimidine,

18% of 2-p-octanoyloxyphenyl-5-octylpyrimidine,

10% of 2-p-hexanoyloxyphenyl-5-octylpyrimidine and

7% of 2-p-nonanoyloxyphenyl-5-octylpyrimidine

can be supercooled to about 0° and has an S_(C) /S_(A) of 52°, an S_(A) /N of 54° and N/I of 56°.

EXAMPLE 23

A liquid crystal phase consisting of

42% of 2-p-decanoyloxyphenyl-5-octylpyrimidine,

23% of 2-p-heptanoyloxyphenyl-5-octylpyrimidine,

18% of 2-p-octanoyloxyphenyl-5-octylpyrimidine,

10% of 2-p-hexanoyloxyphenyl-5-octylpyrimidine,

7% of 2-p-nonanoyloxyphenyl-5-octylpyrimidine and

7% of 2-p-octyloxycarbonylphenyl-5-nonylpyrimidine

can be supercooled to about 0° and has an S_(C) /S_(A) of 46.5°, S_(A) /N of 53° and N/I of 54.5°.

EXAMPLE 24

A liquid crystal phase consisting of 34.5% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

32.5% of 2-p-decyloxyphenyl-5-heptylpyrimidine,

2.0% of 2-p-hexyloxyphenyl-5-nonylpyrimidine,

5.0% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

5.0% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

10.0% of 2-p-hexyloxyphenyl-5-heptylpyrimidine and

11.0% of 2-p-octylphenyl-5-p-pentyloxyphenylpyrimidine

can be supercooled to about 10° and has an S_(C) /S_(A) of 55°, an S_(A) /N of 68.5° and N/I of 75°.

EXAMPLE 25

A liquid crystal phase consisting of

40% of 2-p-decanoyloxyphenyl-5-octylpyrimidine,

20% of 2-p-heptanoyloxyphenyl-5-octylpyrimidine,

20% of 2-p-octanoyloxyphenyl-5-octylpyrimidine,

8% of 2-p-hexanoyloxyphenyl-5-octylpyrimidine,

8% of 2-p-octylphenyl-5-p-pentyloxyphenylpyrimidine and

4% of 2-p-hexylphenyl-5-p-hexyloxyphenylpyrimidine

has an S_(C) /S_(A) of 57.5°, an S_(A) /N of 67° and N/I of 74°.

EXAMPLE 26

A liquid crystal phase consisting of

23% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

18% of 2-p-decyloxyphenyl-5-heptylpyrimidine,

15% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

8% of 2-p-nonanoyloxyphenyl-5-nonylpyrimidine,

8% of 2-p-undecanoyloxyphenyl-5-nonylpyrimidine,

10% of 2-p-octylphenyl-5-p-octyloxyphenylpyrimidine,

7% of 2-p-nonylphenyl-5-p-pentyloxyphenylpyrimidine and

11% of 2-p-pentylphenyl-5-p-hexyloxyphenylpyrimidine

has an S_(C) /S_(A) of 63°, an S_(A) /N of 74° and N/I of 81°.

EXAMPLE 27

A liquid crystal phase consisting of

42% of 2% of 2-p-decanoyloxyphenyl-5-octylpyrimidine,

23% of 3% of 2-p-heptanoyloxyphenyl-5-octylpyrimidine,

18% of 2-p-octanoyloxyphenyl-5-octylpyrimidine,

10% of 2-p-hexanoyloxyphenyl-5-octylpyrimidine and

7% of 2-p-2-oxadodecylphenyl-5-octylpyrimidine

is prepared.

EXAMPLE 28

A liquid crystal phase consisting of

25% of 2-p-decyloxyphenyl-5-heptylpyrimidine,

25% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

10% of 2-p-hexyloxyphenyl-5-nonylpyrimidine,

10% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

11% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

11% of 2-p-heptyloxyphenyl-5-heptylpyrimidine and

8% of 2-p-decyloxyphenyl-5-(trans-4-octylcyclohexyl)pyrimidine

is prepared.

EXAMPLE 29

A liquid crystal phase consisting of

20% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

10% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

18% of 2-p-decyloxyphenyl-5-octylpyrimidine,

15% of 2-p-nonyloxyphenyl-5-octylpyrimidine,

15% of 2-p-octyloxyphenyl-5-octylpyrimidine,

12% of 2-p-heptyloxyphenyl-5-octylpyrimidine and

10% of 2-p-(1,4-dioxaundecyl)-phenyl-5-nonylpyrimidine.

A suitable chiral doping substance can be added to all the achiral base mixtures given as examples, and these can be used as ferroelectric materials.

EXAMPLE 30

A solution of 0.01 m of n-butyl-lithium (15% in n-pentane) is added dropwise to a solution of 0.01 m (2.7 g) of 3-(4-heptyloxyphenyl)-pyridine (which is obtainable by coupling of 4-heptyloxyphenylmagnesium bromide and 3-bromopyridine) in 30 ml of dry toluene at +15° C. under nitrogen. The reaction mixture is then boiled under reflux for a further 4 hours and, after cooling, hydrolysed carefully with 10 ml of water. The organic phase is washed with water and saturated NaCl solution, dried with magnesium sulfate and evaporated. The oily residue is purified by chromatography over a silica gel column with diisopropyl ether as the mobile phase. 2-Butyl-5-p-heptyloxyphenylpyridine, Cr. 80°, is obtained.

EXAMPLE 31

A solution of 0.01 m of 4-heptyloxyphenyllithium, prepared from 4-bromoheptyloxybenzene and lithium, in 30 ml of toluene is added dropwise to a solution of 0.01 m of 3-pentylpyridine, which is obtainable by coupling pentylmagnesium bromide and 3-bromopyridine, in 30 ml of toluene at -20° C. under nitrogen. The reaction mixture is heated at the boiling point for 4 hours and, after cooling, is carefully hydrolysed with 10 ml of water. The organic phase is washed with water and saturated NaCl solution, dried with magnesium sulfate and evaporated. The residue is purified over a silica gel column with diisopropyl ether as the mobile phase. 2-p-Heptyloxy-phenyl-5-pentylpyrimidine is obtained.

The homologous 2-p-alkoxyphenyl-5-alkylpyridines are prepared analogously.

EXAMPLE 32

A liquid crystal phase consisting of

3% of 2-p-hexyloxyphenyl-5-heptylpyrimidine,

6% of 2-p-hexyloxyphenyl-5-nonylpyrimidine,

3% of 2-p-heptyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

20% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

10% of 2-p-(trans-4-propylcyclohexyl)-phenyl-5-pentylpyridine,

25% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-butylcyclohexane,

13% of r-1-cyano-cis-4-(4'-heptylbiphenyl-4-yl)-1-hexylcyclohexane,

5% of r-1-cyano-cis-4-(trans-4-pentylcyclohexyl)-1-(trans-4-pentylcyclohexyl)-cyclohexane and

9% of optically active R-4-(5-hexylpyrimidin-2-yl)-phenyl-2-chloropropionate

displays Cr. -10° Sc* 68° S_(A) * 73° Ch 99° I and spontaneous polarization of 8.1 nC/cm².

EXAMPLE 33

A liquid crystal phase consisting of

3% of 2-p-hexyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-hexyloxyphenyl-5-nonylpyrimidine,

3% of 2-p-heptyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

22% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

21% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-octylcyclohexane,

10% of r-1-cyano-cis-4-(4'-heptylbiphenyl-4-yl)-1-hexylcyclohexane,

5% of 2-p-pentyloxyphenyl-5-hexylpyridine,

5% of 2-p-heptanoylphenyl-5-hexylpyridine,

10% of optically active 1-(4'-pentylbiphenyl-4-yl)-2-(1-cyano-3-methylcyclohexyl)-ethane and

12% of optically active r-1-cyano-cis-4-(4'-heptylbiphenyl-4-yl)-1-(2-methylbutyl)-cyclohexane

exhibits Cr. -15° Sc* 58° S_(A) * 64° Ch 82° I and spontaneous polarization of 20 nC/cm².

EXAMPLE 34

A liquid crystal phase consisting of

3% of 2-p-hexyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-hexyloxyphenyl-5-nonylpyrimidine,

3% of 2-p-heptyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

20% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

3% of 2-p-pentyloxyphenyl-5-hexylpyridine,

3% of 2-p-hexyloxyphenyl-5-hexylpyridine,

3% of 2-p-hexyloxyphenyl-5-octylpyridine,

30% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-octylcyclohexane,

16% of r-1-cyano-cis-4-(4'-heptylbiphenyl-4-yl)-1-hexylcyclohexane and

10% of ethyl 2-[p-(5-nonylpyrimidin-2-yl)-phenoxy]-propanoate (optically active)

exhibits Cr. -21° Sc* 61° S_(A) * 65° Ch 81° I and spontaneous polarization of 9 nC/cm².

EXAMPLE 35

A liquid crystal phase consisting of

30% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

3% of 2-p-hexylmercaptophenyl-5-heptylpyrimidine,

3% of 2-p-heptylmercaptophenyl-5-heptylpyrimidine,

3% of 2-p-octylmercaptophenyl-5-heptylpyrimidine,

11% of r-1-cyano-cis-4-(4'-pentylbiphenyl-4-yl)-1-octylcyclohexane,

10% of r-1-cyano-cis-4-(4'-heptylbiphenyl-4-yl)-1-butylcyclohexane,

20% of r-1-cyano-cis-4-(4'-nonyloxybiphenyl-4-yl)-1-octylcyclohexane and

10% of R-4-(5-hexylpyrimidin-2-yl)-phenyl-2-chloropropionate

exhibits Cr. -10° Sc* 61° S_(A) * 66° Ch 85 I and spontaneous polarization of 12 nC/cm².

EXAMPLE 36

A liquid crystal phase consisting of

3% of 2-p-hexyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-heptyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-hexyloxyphenyl-5-nonylpyrimidine,

20% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

30% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-octylcyclohexane,

10% of r-1-cyano-cis-4-(4'-heptylbiphenyl-4-yl)-1-hexylcyclohexane,

30% of r-1-cyano-cis-4-(4'-octylbiphenyl-4-yl)-1-butylcyclohexane,

3% of p-hexyloxyphenyl 5-heptylpicolinate,

3% of p-hexyloxyphenyl 5-heptyloxypicolinate,

3% of p-octyloxyphenyl 5-nonylpicolinate and

10% of chiral R-4-(5-hexylpyrimid-2-yl)-phenyl 2-chloropropionate

exhibits Cr. -12° Sc* 65° S_(A) * 69° Ch 89° I and spontaneous polarization of 12 nC/cm².

EXAMPLE 37

A liquid crystal phase consisting of

3% of 2-p-hexyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-heptyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-hexyloxyphenyl-5-nonylpyrimidine,

20% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

5% of 2-p-pentyloxyphenyl-5-hexylpyridine,

5% of 2-p-hexyloxyphenyl-5-heptylpyridine,

30% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-octylcyclohexane,

14% of optically active r-1-cyano-cis-4-(4'-heptyloxybiphenyl-4-yl)-1-(2-methylbutyl)-cyclohexane and

11% of optically active 1-(4'-pentylbiphenyl-4-yl)-2-(1-cyano-3-methylcyclohexyl)-ethane

exhibits Cr. -25° Sc* 67° S_(A) * 74° Ch 88° I and spontaneous polarization of 27 nC/cm².

EXAMPLE 38

A liquid crystal phase which consists of

3% of 2-p-hexyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-heptyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-hexyloxyphenyl-5-nonylpyrimidine,

20% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

30% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-octylcyclohexane,

10% of r-1-cyano-cis-4-(4'-heptylbiphenyl-4-yl)-1-hexylcyclohexane,

6% of r-1-cyano-cis-4-(4'-octylbiphenyl-4-yl)-1-butylcyclohexane,

3% of 6-pentyloxypyridazin-3-yl p-hexyloxybenzoate,

3% of 6-heptyloxypyridazin-3-yl p-hexyloxybenzoate,

3% of 6-heptyloxypyridazin-3-yl p-heptyloxybenzoate and

10% of chiral R-4-(5-hexylpyrimid-2-yl)-phenyl 2-chloropropionate

is prepared.

EXAMPLE 39

A liquid crystal phase consisting of

3% of 2-p-hexyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-heptyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-hexyloxyphenyl-5-nonylpyrimidine,

20% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

30% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-octylcyclohexane,

10% of r-1-cyano-cis-4-(4'-heptylbiphenyl-4-yl)-1-hexylcyclohexane,

6% of r-1-cyano-cis-4-(4'-octylbiphenyl-4-yl)-1-butylcyclohexane,

3% of 6-(p-heptyloxyphenyl)-3-hexylpyridazine,

3% of 6-(p-heptyloxyphenyl)-3-heptylpyridazine,

3% of 6-(p-nonyloxyphenyl)-3-heptylpyridazine and

10% of chiral R-4-(5-hexylpyrimid-2-yl)-phenyl 2-chloropropionate

is prepared

EXAMPLE 40

A liquid crystal phase consisting of

3% of 2-p-hexyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-heptyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

20% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

30% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-octylcyclohexane,

10% of r-1-cyano-cis-4-(4'-heptylbiphenyl-4-yl)-1-hexylcyclohexane,

6% of r-1-cyano-cis-4-(4'-octylbiphenyl-4-yl)-1-butylcyclohexane,

3% of 1-(p-heptyloxyphenyl)-2-(5-heptylpyridin-2-yl)-ethane,

3% of 1-(p-nonyloxyphenyl)-2-(5-heptylpyridin-2-yl)-ethane,

3% of 1-(p-nonyloxyphenyl)-2-(5-nonylpyridin-2-yl)-ethane and

10% of chiral R-4-(5-hexylpyrimid-2-yl)-phenyl 2-chloro-propionate

is prepared.

EXAMPLE 41

A liquid crystal phase consisting of

3% of 2-p-hexyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-heptyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-hexyloxyphenyl-5-nonylpyrimidine,

20% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

30% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-octylcyclohexane,

10% of r-1-cyano-cis-4-(4'-heptylbiphenyl-4-yl)-1-hexylcyclohexane,

6% of r-1-cyano-cis-4-(4'-octylbiphenyl-4-yl)-1-butylcyclohexane,

3% of 1-(trans-4-heptylcyclohexyl)-2-(5-heptyloxypyridin-2-yl)-ethane,

3% of 1-(trans-4-heptylcyclohexyl)-2-(5-octyloxypyridin-2-yl)-ethane,

3% of 1-(trans-4-heptylcyclohexyl)-2-(5-nonyloxypyridin-2-yl)-ethane and

10% of chiral R-4-(5-hexylpyrimid-2-yl)-phenyl 2-chloropropionate.

EXAMPLE 42

A liquid crystal phase consisting of

3% of 2-p-hexyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-heptyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-hexyloxyphenyl-5-nonylpyrimidine,

20% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

30% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-octylcyclohexane,

10% of r-1-cyano-cis-4-(4'-heptylbiphenyl-4-yl)-1-hexylcyclohexane,

6% of r-1-cyano-cis-4-(4'-octylbiphenyl-4-yl)-1-butylcyclohexane,

3% of 2-(4'-heptyloxybiphenyl-4-yl)-5-heptylpyrimidine,

3% of 2-(4'-octyloxybiphenyl-4-yl)-5-heptylpyrimidine,

3% of 2-(4'-nonyloxybiphenyl-4-yl)-5-nonylpyrimidine and

10% of chiral R-4-(5-hexylpyrimid-2-yl)-phenyl-2-chloropropionate

is prepared.

EXAMPLE 43

A liquid crystal phase consisting of

3% of 2-p-hexyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-heptyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-hexyloxyphenyl-5-nonylpyrimidine,

20% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

30% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-octylcyclohexane,

10% of r-1-cyano-cis-4-(4'-heptylbiphenyl-4-yl)-1-hexylcyclohexane,

6% of r-1-cyano-cis-4-(4'-octylbiphenyl-4-yl)-1-butylcyclohexane,

3% of 2-(4'-heptyloxybiphenyl-4-yl)-5-heptylpyridine,

3% c 3% of 2-(4'-octyloxybiphenyl-4-yl)-5-heptylpyridine,

3% of 2-(4'-nonyloxybiphenyl-4-yl)-5-nonylpyridine and

10% of chiral R-4-(5-hexylpyrimid-2-yl)-phenyl 2-chloropropionate

is prepared.

EXAMPLE 44

A liquid crystal phase consisting of

3% of 2-p-hexyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-heptyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-hexyloxyphenyl-5-nonylpyrimidine,

20% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

30% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-octylcyclohexane,

10% of r-1-cyano-cis-4-(4'-heptylbiphenyl-4-yl)-1-hexylcyclohexane

6% of r-1-cyano-cis-4-(4'-octylbiphenyl-4-yl)-1-butylcyclohexane,

3% of 2-p-heptyloxyphenyl-5-heptyloxypyrazine,

3% of 2-p-nonyloxyphenyl-5-heptyloxypyrazine,

3% of 2-p-nonyloxyphenyl-5-nonyloxypyrazine and

10% of chiral R-4-(5-hexylpyrimid-2-yl)-phenyl-2-chloropropionate

is prepared.

EXAMPLE 45

A liquid crystal phase consisting of the following racemic compounds:

10% of 2-p-(4-methylhexyloxyphenyl)-5-heptylpyrimidine (m.p. 29°, clear point 60°)

6% of 2-p-(6-methyloctyloxyphenyl)-5-octylpyrimidine (m.p. 3°, clear point 56°)

8% of 2-p-(5-methylheptyloxyphenyl)-5-nonylpyrimidine (m.p. 10°, clear point 59°)

4% of 2-p-(4-methylhexyloxyphenyl)-5-decylpyrimidine (m.p. 3°, clear point 58°,

8% of 2-p-(5-methylheptyloxyphenyl)-5-undecylpyrimidine (m.p. 20°, clear point 59°),

3% of 2-p-(4-methylhexyloxyphenyl)-5-dodecylpyrimidine (m.p. 41°, clear point 62°),

6% of 2-p-(5-methylheptyloxyphenyl)-5-dodecylpyrimidine (m.p. 23°, clear point 62°) and

30% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1octylcyclohexane,

15% of r-1-cyano-cis-4-(4'-octylbiphenyl-4-yl)-1-butylcyclohexane,

and 10% of optically active R-4-(5-hexylpyrimid-2-yl)-phenyl 2-chloropropionate exhibits Cr. -18° Sc* 66° S_(A) * 70° Ch 82° I, spontaneous polarization of 8 nC/cm² and a switching time of 350 ps for 2 pm at 12 V and 20°.

EXAMPLE 46

A liquid crystal phase consisting of the following racemic compounds:

10% of 2-p-(4-methylhexyloxyphenyl)-5-heptylpyrimidine (m.p. 29°, clear point 60°)

6% of 2-p-(6-methyloctyloxyphenyl)-5-octylpyrimidine (m.p. 3°, clear point 56°),

8% of 2-p-(5-methylheptyloxyphenyl)-5-nonylpyrimidine (m.p. 10°, clear point 59°),

4% of 2-p-(4-methylhexyloxyphenyl)-5-decylpyrimidine (m.p. 3°, clear point 58°),

8% of 2-p-(5-methylheptyloxyphenyl)-5-undecylpyrimidine (m.p. 20°, clear point 59°),

3% of 2-p-(4-methylhexyloxyphenyl)-5-dodecylpyrimidine (m.p. 41°, clear point 62°),

6% of 2-p-(5-methylheptyloxyphenyl)-5-dodecylpyrimidine (m.p. 23°, clear point 62°),

30% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-octylcyclohexane,

15% of r-1-cyano-cis-4-(4'-octylbiphenyl-4-yl)-1-butylcyclohexane,

6% of optically active 1-(4'-pentylbiphenyl-4-yl)-2-(1-cyano-3-methylcyclohexyl)-ethane and

4% of optically active 2-octyl p-[p-(5-nonylpyrimid-2-yl)-phenoxymethyl]-benzoate

exibits Cr. -15° Sc* 60° S_(A) * 66° Ch 80° I, spontaneous polarization of 9 nC/cm² and a switching time of 300 μs for 2 μm at 12 V and 20°.

EXAMPLE 47

A liquid crystal phase consisting of

3% of 2-p-hexyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-heptyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-(5-methylheptyloxyphenyl)-5-heptylpyrimidine (racemate),

3% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

7% of 2-p-hexyloxyphenyl-5-nonylpyrimidine,

23% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

32% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-octylcyclohexane,

13% of r-1-cyano-cis-4-(4'-heptylbiphenyl-4-yl)-1-hexylcyclohexane,

3% of r-1-cyano-cis-4-(trans-4-pentylcyclohexyl)-1-(trans-4-pentylcyclohexyl)-cyclohexane and

10% of optically active ethyl 2-[p-(5-nonylpyrimidin-2-yl)-phenoxy] propanoate exhibits Cr. <-30° Sc* 59° S_(A) *.

EXAMPLE 48

A liquid crystal phase consisting of

3% of 2-p-hexyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-heptyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-hexyloxyphenyl-5-nonylpyrimidine,

20% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

15% of r-1-cyano-cis-4-(4'-octylbiphenyl-4-yl)-1-butylcyclohexane,

30% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-octylcyclohexane,

3% of S-(6-nonyloxypyridazin-3-yl p-octylthiobenzoate

7% of optically active 1-(4'-pentylbiphenyl-4-yl)-2-(1-cyano-3-methylcyclohexyl)-ethane and

10% of optically active r-1-cyano-cis-4-(4'-heptyloxybiphenyl-4-yl)-1-(3-methylbutyl)-cyclohexane

exhibits Sc* 63° S_(A) * 66° Ch 84° I and spontaneous polarization of 20 nC/cm².

In the mixtures of optically active materials used in Examples 33, 37, 46 and 48, the addition made in each case is intended to produce a right-handed twist, whereas the other addition is intended to produce a left-handed twist.

EXAMPLE 49

A liquid crystal phase consisting of

3% of 2-p-hexyloxyphenyl-5-octylpyrimidine,

3% of 2-p-heptyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-nonyloxyphenyl-5-heptylpyrimidine,

3% of 2-p-hexyloxyphenyl-5-nonylpyrimidine,

20% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

3% of 3-p-pentyloxyphenyl-6-hexyloxypyridazine,

3% of 3-p-pentyloxyphenyl-6-octyloxypyridazine,

3% of 3-p-hexyloxyphenyl-6-hexyloxypyridazine,

25% of r-1-cyano-cis-4-(4'-octylbiphenyl-4-yl)-1-butylcyclohexane,

10% of r-1-cyano-cis-4-(4'-heptylbiphenyl-4-yl)-1- hexyl-cyclohexane,

5% r-1-cyano-cis-4-(trans-4-pentylcyclohexyl)-1-(trans-4-pentylcyclohexyl)-cyclohexane,

5% of r-1-cyano-cis-4-(4'-nonyloxybiphenyl-4-yl)-1-octylcyclohexane and

11% of optically active ethyl 2-[p-(5-nonylpyrimidin-2-yl)-phenoxy]-propanoate exhibits Sc* 58° S_(A) * 64° Ch 79° I and spontaneous polarization of 8 nC/cm². 

What is claimed is:
 1. In a liquid crystal phase having ferroelectric properties useful for rapidly switching displays and comprising at least two liquid crystalline compounds which form an achiral base mixture having a tiled smectic phase, and a chiral doping substance, the improvement wherein at least one compound of said achiral base mixture is of the formula I

    R.sup.1 -A.sup.1 -A.sup.2 -R.sup.2                         I

wherein R¹ and R² are each alkyl of 1-15 C atoms wherein one or two non-adjacent CH₂ groups can be replaced by --O--, --S--, --CO--, --CO----S--, --S--CO--, and/or --CH═CH--, and A¹ -A² is ##STR27## and wherein at least one compound of said achiral base mixture is of Formula I wherein independently R¹ and R² are as defined above and A¹ -A² is ##STR28##
 2. A phase of claim 1, wherein R¹ is n-heptyl, n-octyl or n-nonyl.
 3. A phase of claim 1, containing at least one compound of formula I having R¹ =n-nonyl and simultaneously at least one compound of formula I wherein R¹ is n-heptyl or n-octyl.
 4. A phase of claim 1, containing at least one compound of formula I wherein R² is n-hexyloxy, n-heptyloxy or n-octyloxy and at least one compound of formula I wherein R² is n-nonyloxy or n-decyloxy.
 5. A phase of claim 4, containing at least one compound of formula I wherein R² is n-heptyloxy or n-octyloxy.
 6. A phase of claim 1, wherein the sum of the C atoms in the groups R¹ and R² is 15 or more.
 7. A phase of claim 6, wherein the sum of the C atoms in the groups R¹ and R² is 15 to
 20. 8. A phase of claim 1, wherein R¹ is n-alkyl of 7 to 10 C atoms and R² is n-alkanoyloxy, n-alkoxycarbonyl or n-alkylthio with in each case 5 to 10 C atoms.
 9. A phase of claim 1, containing at least one compound of formula I wherein R² is n-alkylthio.
 10. A phase of claim 1, containing at least one compound of formula I in which at least one group R¹ or R² is a branched alkyl or alkoxy radical.
 11. A phase of claim 1, containing compounds of the formula I in which R¹ and R² independently of one another are each alkyl, alkoxy, alkanoyloxy, alkoxy-carbonyl or alkoxycarbonyloxy, each having 5 to 12 C atoms.
 12. A phase of claim 11, containing compounds of the formula I in which R¹ and R² independently of one another are each alkyl or alkoxy.
 13. A phase of claim 12, containing compounds of the formula I in which R¹ is alkyl or alkoxy and R² is alkoxy.
 14. A phase of claim 11, containing compounds of the formula I having R¹ and R² groups with a straight-chain alkyl radical.
 15. A phase of claim 11, containing compounds of the formula I in which one of the groups R¹ and R² is alkyl.
 16. A phase of claim 1, containing compounds of the formula I in which R¹ is n-alkyl of 7 to 10 C atoms and R² is --CH₂ O--(CH₂)_(p) --CH₃ or --O--(CH₂)_(q) --O--(CH₂)_(r) --CH₃, wherein p is 4 to 10, q is 1 to 5 and r is 4 to
 10. 17. A phase of claim 1, containing a liquid crystal component with negative dielectric anisotropy.
 18. A phase of claim 17, containing at least one compound containing the structural element A, B or C as the component with negative dielectric anisotropy. ##STR29##
 19. A phase of claim 1, containing at least one compound of the formula II

    R.sup.4 -A.sup.1 -COX-A.sup.2 -R.sup.5                     II

wherein R⁴ and R⁵ are each alkyl of 1-15 C atoms, in each of which one or two non-adjacent CH₂ groups can be replaced by --O--, --CO--, --O--CO--, --CO--O--and/or --CH═CH--, X is O or S and A¹ and A² are each 1,4-phenylene or trans-1,4-cyclohexylene, or one of the groups A¹ and A² is optionally also 4,4'-biphenylyl or trans, trans-4,4'-bicyclohexyl.
 20. A phase of claim 1, containing at least one compound of the formula V

    R.sup.1 -Q.sup.1 -A-(Q.sup.2).sub.q -R.sup.2               V

wherein R¹ and R² independently of one another are each a straight-chain alkyl group of 1 to 15 C atoms, wherein one or more non-adjacent CH₂ --groups may be replaced by --O--, --S--, --CO--, --CHCH₃ --O--, --CHCH₃ --, --CH-halogen--, --CHCN--, --O--CO--, --O--COO--, --CO--O--and/or --CH═CH--, A is ##STR30## q is 0 or 1, Q¹ and Q² independently of one another are each --(A°--Z°)_(p) --,wherein A° is 1,4-cyclohexylene which is unsubstituted or mono-substituted or polysubstituted by halogen atoms, CH₃ groups and/or nitrile groups, and wherein furthermore one or two non-adjacent CH₂ groups may be replaced by --O--and/or --S--and/or a ##STR31## may be replaced by ##STR32## or is 1,4-phenylene which is unsubstituted or monosubstituted or polysubstituted by halogen atoms, CH₃ groups and/or nitrile groups, wherein furthermore one or more CH groups may be replaced by N (Ph), and one of the radicals A° may furthermore be 2,6-naphthylene (Na) or tetrahydro-2,5-naphthylene (4H-Na), both optionally substituted by halogen or CN, Z°, Z¹ and Z² independently of one another are each --CO--O--, --O--CO--, --CH₂ O--, --OCH₂ --, CH₂ CH₂ --, --CHCN--CH₂ --, --CH₂ --CHCN-- or a single bond, and p is 1, 2 or 3, or when A is tetra- or octahydrophenanthrene, also 0,and wherein when A is ##STR33## at least one group Z° is --CHCN--CH₂ --or --CH₂ --CHCN-- and/or at least one CH₂ group in at least one of the groups R¹ and R² is replaced by --CHCN--.
 21. A phase of claim 20, containing achiral compounds of the formula V and doped with chiral compounds of the formula I or additionally with other chiral compounds.
 22. A phase of claim 20, containing at least one compound of the formulae V1 to V18: ##STR34##
 23. A phase of claim 20, containing at least one compound of the formulae V19 to V22:

    R.sup.1 -A°-Cy-(CH.sub.2).sub.r -CHCN-C.sub.s H.sub.2s+1 V 19

    R.sup.1 -A°-A°-Cy-(CH.sub.2).sub.r -CHCN-C.sub.s H.sub.2s+1 V 20

    R.sup.1 -A°-A°-CHCN-CH.sub.2 -Cy-R.sup.2     V 21

    R.sup.1 -A°-A°-CH.sub.2 -CHCN-Cy-R.sup.2     V 22

wherein r is 0, 1, 2 or 3 and (r+s) is 1 to
 14. 24. A phase of claim 1, containing at least three compounds of formula I.
 25. A phase of claim 24, containing at least five compounds of formula I.
 26. A phase of claim 1, containing at least one other component with a negative or low positive dielectric anisotropy.
 27. A phase of claim 26, wherein this (these) other component(s) make up 1 to 50% of the total phase.
 28. A phase of claim 26, wherein the other component(s) is (are) of the formulae IIa to IIi: ##STR35## wherein R⁴ and R⁵ are in each case straight-chain alkyl, alkoxy, alkanoyloxy or alkoxycarbonyl with in each case 3 to 12 C atoms, X is O or S, and in the compounds of the formulae IIa, IIb, IId, IIe, IIf and IIg, a 1,4-phenylene group is optionally laterally substituted by halogen or CN.
 29. A phase of claim 28, containing compounds of the part formulae IIa, IIb, IId or IIf, wherein R⁴ and R⁵ are each straight-chain alkyl or alkoxy in each case of 5 to 10 C atoms.
 30. A phase of claim 28, containing at least one of the individual compounds shown in the following table:

    ______________________________________                                         Formula     R.sup.4     R.sup.5    X                                           ______________________________________                                         IIa         n-Decyloxy  n-Heptyloxy                                                                               ◯                               IIa         n-Hexyloxy  n-Decyloxy ◯                               IIa         n-Octyloxy  n-Heptyl   ◯                               IIa         n-Octyloxy  n-Pentyl   ◯                               IIa         n-Decyloxy  n-Heptyl   ◯                               IIa         n-Decyloxy  n-Pentyl   ◯                               IIf         n-Pentyl    n-Pentyl   ◯                               IIf         n-Pentyl    n-Hexyl    ◯                               ______________________________________                                    


31. A phase of claim 1, containing at least one compound of the formula ##STR36## wherein R⁴ and R⁵ are straight-chain alkyl of 2 to 7 C atoms.
 32. A phase of claim 1, containing at least one compound of the formula

    R'-Q.sup.3 -Q.sup.4 -R'''                                  IIIc

wherein R' is a straight-chain alkyl or alkoxy group in each case of 2 to 10 C atoms, Q³ and Q⁴ are each 1,4-phenylene, 4,4'-biphenylyl or trans-1,4-cyclohexylene, and one of the groups Q³ and Q⁴ can also be 1,4-phenylene, wherein at least one CH group is replaced by N, R''' is an optically active radical with an asymmetric carbon atom of the structure ##STR37##
 33. A phase of claim 32, containing at least one compound of the formula IIIc': ##STR38## wherein A is 1,4-phenylene or trans-1,4-cyclohexylene and n is 0 or
 1. 34. A phase of claim 33, wherein A is 1,4-phenylene and n is
 1. 35. A phase of claim 1, containing at least one chiral compound of the formulae ##STR39## wherein R⁴ and R⁵ are each independently alkyl, alkoxy, alkanoyloxy or alkoxycarbonyl in each case of 3 to 12 C atoms and X is O or S.
 36. A phase of claim 1, containing at least one compound of formula I wherein R¹ and R² are each independently alkyl of 5 to 12 C atoms or alkyl of 5 to 12 C atoms, wherein one CH₂ group is replaced by --O--, --S--, --CO--, --O--CO--, --CO--O--, --CO--S--, --S--CO--or --CH═CH--.
 37. A phase of claim 1, containing at least one of the following compounds:2-p-decyloxyphenyl-5-heptylpyrimidine, 2-p-nonyloxyphenyl-5-nonylpyrimidine, 2-p-hexyloxyphenyl-5-nonylpyrimidine, 2-p-nonyloxyphenyl-5-heptylpyrimidine, 2-p-octyloxyphenyl-5-heptylpyrimidine, 2-p-heptyloxyphenyl-5-heptylpyrimidine, 2-p-hexyloxyphenyl-5-heptylpyrimidine, 2-p-decyloxyphenyl-5-nonylpyrimidine, 2-p-heptyloxyphenyl-5-nonylpyrimidine, 2-p-octyloxyphenyl-5-nonylpyrimidine, 2-p-decyloxyphenyl-5-octylpyrimidine, 2-p-nonyloxyphenyl-5-octylpyrimidine, 2-p-octyloxyphenyl-5-octylpyrimidine, 2-p-heptyloxyphenyl-5-octylpyrimidine or 2-p-hexyloxyphenyl-5-octylpyrimidine.
 38. A phase of claim 1, containing at least one of the following compounds:2-(4'-heptyloxybiphenyl-4-yl)-5-heptylpyrimidine, 2-(4'-octyloxybiphenyl-3-yl)-5-heptylpyrimidine, or 2-(4'-nonyloxybiphenyl-4-yl)-5-nonylpyrimidine.
 39. A phase of claim 1, containing at least one compound of formula I in which one of R¹ and R² is 4-methylhexyloxy, 5-methylheptyloxy or 6-methyloctyloxy and the other group R¹ or R² is a straight-chain alkyl group.
 40. A phase of claim 39, containing at least one of the following compounds:2-p-(4-methylhexyloxyphenyl)-5-heptylpyrimidine, 2-p-(6-methyloctyloxyphenyl)-5-octylpyrimidine, 2-p-(5-methylheptyloxyphenyl)-5-nonylpyrimidine, 2-p-(4-methylhexyloxyphenyl)-5-decylpyrimidine, 2-p-(5-methylheptyloxyphenyl)-5-undecylpyrimidine, 2-p-(4-methylhexyloxyphenyl)-5-dodecylpyrimidine or 2-p-(5-methylheptyloxyphenyl)-5-dodecylpyrimidine.
 41. A phase of claim 24, containing at least three achiral compounds of formula I.
 42. A phase of claim 25 containing at least five achiral compounds of formula I.
 43. In a ferroelectric electrooptical display element comprising a liquid crystal phase having ferroelectric properties, the improvement wherein the phase is one of claim
 1. 44. A ferroelectric display element of claim 43 operating by the SSFLC mechanism.
 45. A phase of claim 1, wherein each of R¹ and R² independently is alkyl or alkyl wherein one CH₂ group is replaced by oxygen.
 46. A phase of claim 1, wherein in said second compound of Formula I, A¹ -A² is ##STR40##
 47. A phase of claim 1, wherein in said second compound of formula I, A¹ -A² is ##STR41## 